1. Field of the Invention
The present invention relates to a sheet stacking apparatus, a method for controlling the same, and a storage medium.
2. Description of the Related Art
There is conventionally a sheet stacking apparatus that includes a stacking tray for stacking sheets and lowers a discharge tray according to the stacked amount of sheets to be discharged.
Specifically, as illustrated in FIG. 11A, the discharge tray is lowered in response to discharging and stacking of sheets on the discharge tray. After a sheet bundle has been removed, the discharge tray is raised to a normal position. On the other hand, as illustrated in FIG. 11B, when the discharge tray is at the normal position (state illustrated in FIG. 11A), a space is present below the discharge tray. However, as illustrated in FIG. 11B, when an obstacle is located below the discharge tray, the discharge tray may collide with the obstacle while sheets are discharged to the tray. Therefore, there is known a method for detecting such a state, in which the obstacle prevents the discharge tray from lowering, and stopping the sheet discharging to the discharge tray or the lowering of the discharge tray to display a warning on an operation unit (as discussed in Japanese Patent Application Laid-Open No. 2001-226022).
As discussed in Japanese Patent Application Laid-Open No. 2001-226022, after the warning has been displayed to a user, the user may try to remove the obstacle. However, the discharge tray and the obstacle are kept in a contact state because the lowering of the discharge tray has been interrupted by the obstacle. When the user tries to remove the obstacle in this state, a load is applied to the obstacle or the discharge tray. There is a possibility that the obstacle may be deformed or the discharge tray may be destroyed.